Research On Design And Characteristics Of Enhanced Constrained Damping Materials And Structures

Nitrile Butadiene Rubber?NBR?,having high damping performance,excellent oil resistance and heat aging resistance,is used as a vibration and noise reduction material for mechanical equipment in underwater vehicles and ships.Limited by effective damping temperature range,the single-component nitrile rubber materials can hardly meet the needs of damping performance materials for ships and underwater vehicles.Due to the limitation of internal space and load,the ship urgently needs a damping composite structure with small volume and excellent damping effect.In this paper,Phenol-formaldehyde?PF?resin was applied to modify NBR to prepare elastic composite materials with wide temperature range and good damping performance.An enhanced constrained layer damping?ECLD?structure was invented.NBR/PF composite material was used as the perforated viscoelastic damping material?PVDM?to improve the damping efficiency.At the same time,the research and optimization on the vibration suppression mechanism and effectiveness of the ECLD were carried out.Finally,graphene oxide?GO?modified NBR was used to enhance its damping performance,thermal conductivity and anti-fatigue life.Firstly,the phenolic-formaldehyde?PF 2123-3?resin that can raise the glass transition temperature?T_g?was selected to mix with NBR.By adjusting the NBR/PF ratio,elastic damping materials with wide temperature range,high damping performance,excellent mechanical properties were prepared.The results showed that when the amount of PF increased,the T_gof the material increased,the effective damping temperature range??T?was widened and the mechanical properties were improved.In addition,the good elasticity was maintained,which facilitated the close fitting of curved surfaces and irregular-shaped structures.When the amount of PF added was 30 phr,T_gincreased from 9.1 ^oC to 30.9 ^oC.?T was widened from 36.9 ^oC to 45.8 ^oC.Tensile strength was increased by 4.8 MPa,an increase of 35%.Elongation at break reached 780%.The NBR/PF elastic composite material had excellent performance and was able to meet the application requirements of the ship cabin.Then,an ECLD structure was invented and a free beam vibration test system was designed.In addition,the damping performance of the ECLD structure was studied and optimized.The results showed that the ECLD structure exceeded the damping capabilities limits of the unconstrained layer damping?UCLD?and passive constrained layer damping?PCLD?.With the increase of the constraining force,the damping efficiency of the ECLD structure increased and the high-damping temperature range was broadened.When the constrained force was 15 N·m and the thickness of perforated viscoelastic damping material is12 mm,the maximum difference of vibration acceleration level(VALD_max)was 14.80 d B;the high-damping temperature range reached 43.6 ^oC,which was broadened by 27.1 ^oC.The modal tests showed that the ECLD structure was able to suppress all the formants,change its third-and fourth-order formants in mode shape and decrease the amplitude.Furthermore,most of the high-order modal formants disappeared.When the thickness of the damping layer was only 4 mm,the VALD_maxof the ECLD structure reached 10.43 d B,8.72 d B and 3.00 d B higher than those of UCLD and PCLD,respectively.Besides,the acceleration response amplitude was reduced by 63.4%and 29.2%,respectively.Its damping property had exceeded8 mm thick PCLD structure and was closed to 16 mm thick UCLD structure.The efficient damping of ECLD structure was suitable for ships and underwater vehicles restricted by space and load.Products using this technology have been equipped in batches and alternative imports.Finally,an improved solution blending method was used to prepare nitrile NBR/GO elastic composites with high damping performance,high thermal conductivity and high anti-fatigue life.The results showed that GO was evenly dispersed,and its damping performance,thermal conductivity,electrical conductivity,mechanical properties and anti-fatigue life were improved.When the amount of PF added was 1.0 phr,the T_gwas increased by 1.7 ^oC;the maximum loss factor was 1.79;the thermal conductivity increased from 0.126 W/?m·k?to 0.236 W/?m·k?;the tensile strength increased from 11.4 MPa to 17.1MPa;the conductivity increased by 14.5 times;the anti-fatigue life corresponding of 90%of the loss modulus increased from 4800 times to 17500 times;the anti-fatigue life corresponding of 80%of the loss modulus increased from 14800 times to 36600 times,which mean that the materials had longer service life.